You need to have a pesticide license to apply herbicides or crabgrass pre-emergent.
Lucky you have Gregson Clark just down the road. Top quality sprayers and people. They can explain what you need. If you buy a ride-on, you can use the sprayer as a nurse tank to fill the ride-on.
I don't recommend a tow-behind sprayer, as they are a difficult to maneuver in small areas with bushes, flower beds, or islands.